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 Post subject: Reefed sail trim upwind.
PostPosted: Tue May 26, 2009 8:07 am 
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I notice that when reefed, the sail trim is off such that the leech is open. If I pull down on the clew or even drape my arm over it, it trims much better.

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PostPosted: Wed May 27, 2009 5:44 am 
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The open leech or sail twist as I have heard it called helps depower the sail which is the intention of reefing. If you effectively move the sheeting angle forward you repower the top of the sail move the center of effort upward and defeat some of the benifits of the reef. Contrary to what some people might think or what is aesthetically pleasing some luff on the forward part of the sail or the upper part of the sail can be bennificial to upwind performance. I find that when the wind comes up and I start to experience weather helm if I pinch up a bit and let the sheet out a bit allowing the forward part of the sail to luff a bit that the pressure will come off the helm and the boat will point slightly higher and move a bit faster. If the wind is gusty or is still overpowering the rig then it is probably time to throw in a bit of a reef.


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PostPosted: Thu May 28, 2009 4:53 am 
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Opening the leech does help depower the sail, but you have already done that with the reef. If you are sailing off the wind, no problem. If you are trying to sail close hauled and are trying to make way to weather, it is best to trim the sail properly.

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PostPosted: Thu May 28, 2009 5:16 am 
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Location: Seal Beach California
if you get a boom and boom vang you can solve the problem. Also the improved sail shape this gives allowes sailing in higher winds with out reefing


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PostPosted: Thu May 28, 2009 5:33 am 
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Or you can rig a little tweaker line with a cleat. Mostly the sail shape is fine, as this isn't a competition. But occasionally if you want to "make" a point without tacking, having your arm hang over the mainsheet can give you the trim you need to sail closer to the wind, and faster.

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PostPosted: Fri May 29, 2009 3:35 am 
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JZK. again I say pretty sail trim in high wind conditions is not a prerequisite for going fast and pointing higher upwind. The nice thing about the AI sail is that there are no fixed reef points and you can let the reef out till the boat is just slightly over powered and carry some luff and yes a bit of twist and be more efficient upwind than the person who is carrying more reef with a pretty shaped sail and perfectly streaming teltales. MRL Boom vangs are primarily used for powering up the sail on reaches. You will also be in a good position to sail though the lulls. This works on all craft from dinghys to 60 ft steelhulls. I won't list my sailing credentials here but I will say that chekika can attest to my upwind sailing abilities in high winds.


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PostPosted: Fri May 29, 2009 4:33 am 
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Well my friend, having good trim upwind is not about "pretty" but rather about fluid dynamics. As one who races sailboats and who has a background in fluid dynamics, I can attest that a sailboat will go upwind best with proper sail trim. One "tip" to achieve such is to pull down on the clew or hang your arm over the sheet. What is so nice about the AI is that if you, all of a sudden, become overpowered and feel the need to go back to the twist, you are certainly free to release your hand from the clew or move your arm from the sheet, and then you will be depowered. But of course, the point was just to offer a tip for some to try. If you don't want to try it, of course no one will make you.

I have also noticed that the AI is very sensitive to proper sail trim.

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PostPosted: Fri May 29, 2009 6:59 am 
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Location: Calga NSW, Australia
I have no credentials either in sailboat racing or in fluid dynamics, but I have observed a bit of what both jzk and quirkster are talking about and I have been trying to assimilate it.

1. I had noticed that easing the mainsheet until the sail begins to luff, then pulling down on the clew seems to improve performance on both a close and a broad reach in lighter wind, but it has not seemed to make as much difference in stronger winds.

2. In stronger winds, when the boat starts to develop weather helm, I have found that easing the mainsheet usually brings the boat into balance, although the sail trim is not "perfect" in terms of the windward telltale streaming. As the wind gets stronger, I have found there comes a point where, to counteract weather helm, the sail needs to be eased to the point where it is really luffing (ie flapping around). I have taken this as the signal that I need to reef the sail somewhat. This also seems to be about the point where the daggerboard actually starts to make a difference. I like this technique of using the sail trim to counteract weather helm in gusty conditions as it is a pain reefing and unreefing the sail as the windspeed varies.

These are just my observations and I make no pretence to expertise in these matters. I would like to ask quirkster how much he feels the sail should be allowed to luff when sailing close to the wind. I confess to having an instinctive liking for a neatly trimmed sail - at least not flapping around, but I'm open to advice.

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PostPosted: Fri May 29, 2009 7:51 am 
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I never make any claim to being any kind of a sailor, but I do know that Quirkster runs circles around me. He also does very well sailing to weather. I hope to learn a lot from him when we get out on camping trips.

Keith

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PostPosted: Sun May 31, 2009 7:40 am 
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Quirrkster,
Not trying to challenge your sailing background which I am sure is exstensive. However, the unstayed cat rig to me resembles a Finn or a laser on those boats on uses a lot of vang upwind ( even more than on reaches to induce mast bend which flattens the sail. Another benifit from the boom is the abaility to have an outhaul which allowes the sail to be kept flat even when the mainsheet is eased slightly in puffs.
Mike


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